As mentioned, crawl spaces are plenty scary, all by themselves.
My favorite story comes from "Field and Stream," in an article titled "An Asp With Class."
Seems the gent had a summer cabin, upon which he did his own maintenance. Over the course of several summers, he became acquainted with the snake that lived, and grew, under the cabin. The snake would even crawl near him as he worked, watching his every move with great curiosity.
Well, along came the day when he had a problem he could not handle himself. Calling the local plumber, the father & son team wasted no time performing the 'plumbers' wiggle' to squeeze through the hatch, and into the crawl.
He forgot to mention the snake.
A few minutes later, he hears screams from beneath the cabin, followed by the rocketing of the plumbers back out of the hatch .... leaving a very confused snake behind. Heck, he was only trying to be friendly....